1. Field of the Invention
The invention relates generally to the field of hydrocarbon production. More specifically, the present invention relates to a power source for use within a wellbore.
2. Description of Related Art
Recent advancements in the field of oil and gas exploration and production have produced devices requiring a constant source of power. Typically, these devices are powered through a dedicated power supply that is in electrical communication with these devices. One example of a device requiring downhole power includes acoustic signal producers that are disposed downhole for identification of casing perimeters such as defects and/or location of casing collars. Other examples of energy consuming devices downhole include sensors disposed within a casing for monitoring fluid flow parameters, such as pressure, temperature, and flow rate. Additional sensors include an optical sensor, an electromagnetic energy sensor or an acoustic sensor. Optionally, these devices might also be utilized for measuring fluid viscosity and density as well. With the advent of reservoir management techniques, sophisticated monitoring and valving has been integrated in downhole casing. Thus certain portions of a subterranean formation can be produced while at the same time sealing off other portions of the formation by virtue of controlling these valves. The flow monitors and flow control systems are other examples of devices that require an external power source while disposed downhole.
Telemetry systems, such as acoustic and electromagnetic, are additional downhole devices that may be powered with a downhole power supply. These systems include means for generating a seismic signal downhole that travels up the borehole where the resulting signal is received and collected for additional analysis. Additional acoustic devices include transmitters and receivers, such as piezoelectric, electromagnetic acoustic transducers, a pulse laser, signal transmitter, signal receiver and flexural resonators.
The field of downhole ballistics also employs utilization of downhole electrical current. One example of a downhole ballistics device is a perforating gun having shaped charges stored therein. The shaped charges of the perforating guns are typically initiated electrically via an initiation circuit disposed within the perforating gun. Moreover these perforating guns can be oriented within the wellbore with an orientation device, wherein the orientation device can be electrically or mechanically actuated. It should be pointed out that the list of devices using electrical current provided herein is merely a sampling and is not meant to be an exhaustive list.
Power supplies for downhole use currently includes batteries, voltaic cells, wireline transmission, and downhole motors. Examples of downhole motors can be found in U.S. Pat. No. 6,554,074 issued to Longbottom, U.S. Pat. No. 6,745,844 issued to Henderson, and U.S. Pat. No. 6,672,409 issued to Dock, et al. However each of these devices suffers from one of more of the following drawbacks. For example, for use within a wellbore any device must be able to withstand the harsh environment experienced downhole. Often the temperatures downhole can exceed over 100° C. Thus a limited number of batteries are applicable for such use, for example lithium has been found to be a useful battery component. However lithium can be toxic and lithium batteries also are susceptible to exploding. Furthermore, batteries made from lithium can be quite expensive and they are not rechargeable.
With regard to wireline supplied power downhole, additional limitations exist by using this as an electrical source. For example, the diameter of the wireline is limited due to weight constraints, which limits the amount of electrical current that can flow through the wireline. Additionally, the wireline is also used for transmitting data to and from the downhole tool to which the wireline is attached. This further limits the amount of current that can reasonably be transmitted along the wireline. An additional limitation of wireline is that it is used in conjunction with some sort of wireline tool, such as an acoustic or perforating device. Thus with regard to devices involved in reservoir management, such the sensors and valving described above, a wireline source of electrical current would be inappropriate.
With regard to downhole motors, these typically rely upon a flow of either drilling mud or production fluid past a turbine in order to generate either electrical or mechanical power. These devices tend to be somewhat bulky thereby consuming a large amount of space when disposed within the wellbore. Moreover, since these devices require the flow of fluid, they are not operative without a substantial amount of fluid flow within the wellbore. Since there are periods of time with limited or no flow through the wellbore, these devices are limited in the time that they may be able to operate. Additionally, since these require the flow of fluid they necessarily produce a pressure drop of wellbore fluid flow, which has other undesirable affects during exploration and/or production. Therefore there exists a need for a device that can supply downhole power at the harsh downhole environment without hindering otherwise normal exploration and production activities. Moreover, there exists a need for the use of a downhole power source that can be utilized without the requirements of large weight and/or volume.